The unique appeal of the Batman franchise is simple - a superhero with no super powers.

Heath Ledgeras the Joker

It's the aspiring superhero's DIY opportunity. According to the Chicago Tribune, you can become the noble vigilante for a city of your choice for the paltry sum of $7.7 million.

The cost includes a military-grade suit and helmet, night-goggles, grappling-hook gun, cape, Batmobile, armour plating, penthouse suite, bat-signal spotlight, butler and combat training. But you'll require not only the nerve to jump off towering skyscrapers, but also the courage to plumb the depths of human darkness. As the latest movie instalment of this saga explores, even Batman struggles to rise above the pit of human vices.

The Dark Knight (2008), directed by Christopher Nolan, is the second instalment in the re-invention of the DC comic-book series, following on from Batman Begins (2005).

New menace

Gotham city is threatened by a new menace in the form of the elusive Joker (Heath Ledger). Lieutenant Jim Gordon (Gary Oldman) and a reluctant district attorney Harvey Dent (Aaron Eckhart) join forces with Batman (Christian Bale) in combating Gotham's new evil.

Sir Michael Caine reappears as Alfred Pennyworth, the tortured hero's butler and trusted advisor, while Maggie Gyllenhaal reprises Katie Holmes's original role in the first movie as the romantic interest of Batman's alter ego Bruce Wayne. This develops into a love triangle with Harvey Dent.

The Dark Knight is a solid sequel complete with stunning action sequences. However, the intense character of the Joker gives this film an edge with a sheer drop into anarchy. The ensuing battle to end his reign of terror in Gotham becomes itself a reign of terror.

A self-confessed "agent of chaos", the Joker seeks to expose the crazed evil in Gotham which he believes every person capable of. Violent bank robberies, kidnapping, murders - crimes which modernity has de-sensitised us to - are forced upon the viewer as a raw reality.

The Joker is a villain like no other in popular culture. Although he is unpredictable, he is fully in control of events and all his intentions are deadly. Time magazine calls him "one of the most twisted and mesmerising creeps in movie history".

As such, Batman struggles with a totally erratic, unemotional and unresponsive foe. As the butler Alfred tries to explain to Bruce Wayne: "Some men aren't looking for anything logical, like money. They can't be bought, bullied, reasoned or negotiated with. Some men just want to watch the world burn." The Joker gleefully relishes tearing down everything the citizens of Gotham believe in, and pits them against each other and the one person who can save them.

In an emotionally gripping and crucial scene, two ships carrying evacuees from Gotham are hijacked by the Joker. The evacuees both face the same dilemma: they can only be spared by blowing up the other ship. Ironically, it is the perceived "scum" of Gotham, the prisoners, who first refuse to give in to the Joker's sadistic whim. It is the first time that events surprise the Joker. In a time when the only absolute is terror, the light of "decency" so despised by the terrorist is still present.

An equally complex but underdeveloped character in the film is that of Harvey Dent. His transformation into the villain Two-Face is terrifying though touched with classical tragedy. As Gotham's White Knight, he strives to bring integrity to a crumbling belief system; yet, by his descent, its very existence is threatened.

His words echo a bleak outlook: "You thought we could be decent men in an indecent world. But you were wrong. The world is cruel, and the only morality in a cruel world is chance." There are indeed no certainties in a world where anarchy has free reign, but there is a chance of salvation.

This cinema masterpiece has smashed box office records around the world and received critical acclaim, including from the US Conference of Catholic Bishops' Office for Film and Broadcasting.

The film gained much publicity by the untimely death of Heath Ledger, and his final performance does not disappoint. His portrayal of the Joker is chilling and exact, and he has already been tipped by many for an Oscar nomination.

Terrifying scenes

Veteran actors Morgan Freeman and Sir Michael Caine are excellent, Gary Oldman shines in his underrated role, and Christian Bale and Aaron Eckhart both convincingly portray the humanity of their tortured characters. The film may be highly recommended for mature audiences, but be prepared for some terrifying scenes.

Towards the end of the movie, the Joker proclaims that "madness, as you know, is like gravity. All it takes is a little... push".

The Dark Knight is an unnerving, intense and dark investigation of how irreversible this force of gravity really is.